Adelaide: Having been portrayed as a villain in Australia all week, South Africa skipper Faf du Plessis decided to play the role to its fullest with a piece of tactical gamesmanship after scoring another unbeaten century.

The Adelaide oval during the evening session of the 3rd Test between Australia and South Africa. AFP

Booed as he went to the crease on Thursday with South Africa in trouble at 44-3, du Plessis extended his impregnable run at the Adelaide Oval with 118 not out. He declared the innings at 259-9, about 40 minutes from stumps on day one of the day-night test, because he knew it would force another reshuffle of Australia's batting order.

Du Plessis was the player of the match on his test debut when he batted the entire last day for an unbeaten 110 to salvage a series-swinging draw at Adelaide in 2012. He was easily the player of the day on his return to the venue.

With David Warner not allowed to open the batting for Australia because he'd been off the field for too long getting treatment, Usman Khawaja moved up to partner 20-year-old newcomer Matt Renshaw. They navigated 12 overs under lights to reach stumps at 14 without loss, with Renshaw on 8 and Khawaja on 3.

Renshaw was one of three new caps rushed into the XI among five changes after a heavy defeat in Hobart last week that gave South Africa a series-clinching 2-0 lead.

That caused upheaval for Australia and du Plessis, who was fined but avoided a suspension after being found guilty by the International Cricket Council of ball tampering in the second test.

Du Plessis admitted having a mint in his mouth when he licked his fingers to shine the ball in Hobart, but disputed the finding against him and said he'd been unfairly cast as a cheat for doing something that cricketers all over the world have done for years. He even commended Australia skipper Steve Smith for admitting all teams shine the ball using similar methods.

Yet the local newspaper headlines screamed cheat, and the 30,000-plus crowd reacted by loudly booing as du Plessis strode out to bat, and again even when he reached his 100.

"I was expecting a little bit of hostility, but not to that extent," du Plessis said. "To be really honest when I got to 100 I wasn't expecting to still get booed, so that was pretty disappointing."

Australia won the first ever day-night test match in a low-scoring outcome against New Zealand here last year, when the highest total was 224. And when Australia's new-ball pair Josh Hazlewood (4-68) and Mitch Starc (2-78) were swinging the ball early, it created all kinds of trouble for the South African batsmen who were facing the pink ball for the first time in a test.

Three wickets fell in the first session and four in the second, but du Plessis kept the innings moving in partnerships with Stephen Cook (40) and lower-order batsmen Quinton de Kock (24), Kyle Abbott (17) and No. 11 Tabraiz Shamsi.

Under the circumstances, du Plessis said his sixth test century was his finest.

"It was a big day for me to stand up as a captain and make sure I led from the front," he said. "To get through in the manner that I did makes me really proud.

"It was a character test, and the only way I could do it was by scoring runs."

Du Plessis said he felt like he could have kept batting all week, but when he heard the umpires tell Warner that he needed to field for another six minutes before he'd be eligible to open Australia's innings, he knew it was time to gamble.

"I was so driven but the position of the game, it was time for us to declare," he said. "There was a lot of talk about the pink ball at night, so it was a great opportunity to try and at least make a positive move.

"It was just for me to take them a little bit out of their comfort zone and put someone else to open the batting."